We used to bake potatoes in piles of grass from when my dad mowed the lawn. wrap your potato in tinfoil twice and bury it at the bottom of a large grass pile in the morning and come back at the end of the day. the grass gets so hot as it starts to breakdown. this is I think due to fermentation inside the grass mound and the insulation of the outer layers.

It might have been a day or so after the grass had been cut rather than that day.

I don't know how safe or clean it was, or how long it actually took to cook, or whether or not you _should_ do this, but we did, and it worked at least a few times